<!-- 基于better-scroll的轮播图 -->
<template>
	<div class="slider" ref="slider">
		<div class="slider-group" ref="sliderGroup">
			<slot></slot>
		</div>
		<div class="dots">
			<span class="dot" v-for="(item,index) in dots" :key="index" :class="{'active':currentPageIndex === index}"></span>
		</div>
	</div>
</template>

<script type="text/ecmascript-6">
import { addClass } from "common/js/dom";
import BScroll from "better-scroll";

export default {
    name: "slider",
    props: {
        // 循环轮播
        loop: {
            type: Boolean,
            default: true
        },
        // 自动轮播
        autoPlay: {
            type: Boolean,
            default: true
        },
        // 轮播间隔
        interval: {
            type: Number,
            default: 4000
        }
    },
    data() {
        return {
            dots: [],
            currentPageIndex: 0 // 当前第几页
        };
    },
    mounted() {
        setTimeout(() => {
            this._setSliderWidth();
            this._initDots();
            this._initSlider();
            if (this.autoPlay) {
                this._play();
            }
        }, 20);

        // 窗口变化时重新刷新轮播
        window.addEventListener("resize", () => {
            if (!this.slider) {
                return;
            }
            this._setSliderWidth(true);
            this.slider.refresh(); // 刷新slider
        });
    },
    activated() {
        if (this.autoPlay) {
            this._play();
        }
    },
    deactivated() {
        clearTimeout(this.timer);
    },
    beforeDestroy() {
        clearTimeout(this.timer);
    },
    methods: {
        // 设置slider-group的宽度
        _setSliderWidth(isResize) {
            this.children = this.$refs.sliderGroup.children;
            let width = 0;
            let sliderWidth = this.$refs.slider.clientWidth;
            for (let i = 0; i < this.children.length; i++) {
                let child = this.children[i];
                // 给每个子元素添加 class="slider-item"
                addClass(child, "slider-item");
                child.style.width = sliderWidth + "px";
                width += sliderWidth;
            }
            if (this.loop && !isResize) {
                width += 2 * sliderWidth;
            }
            this.$refs.sliderGroup.style.width = width + "px";
        },
        // 初始化轮播图
        _initSlider() {
            this.slider = new BScroll(this.$refs.slider, {
                scrollX: true,
                scrollY: false,
                momentum: false,
                snap: true,
                snapLoop: this.loop,
                snapThreshold: 0.3,
                snapSpeed: 400
            });

            // 当前第几页
            this.slider.on("scrollEnd", () => {
                let pageIndex = this.slider.getCurrentPage().pageX;
                if (this.loop) {
                    pageIndex -= 1;
                }
                this.currentPageIndex = pageIndex;

                if (this.autoPlay) {
                    this._play();
                }
            });

            this.slider.on("beforeScrollStart", () => {
                if (this.autoPlay) {
                    clearTimeout(this.timer);
                }
            });
        },
        // 轮播图中的点点
        _initDots() {
            this.dots = new Array(this.children.length);
        },
        // 自动轮播
        _play() {
            let pageIndex = this.currentPageIndex + 1;
            if (this.loop) {
                pageIndex += 1;
            }
            this.timer = setTimeout(() => {
                this.slider.goToPage(pageIndex, 0, 400);
            }, this.interval);
        }
    }
};
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~common/stylus/variable'
.slider
	min-height 1px
	.slider-group
		position relative
		overflow hidden
		white-space nowrap
		.slider-item
			float left
			box-sizing border-box
			overflow hidden
			text-align center
			a
				display block
				width 100%
				overflow hidden
				text-decoration none
			img
				display block
				width 100%
	.dots
		position absolute
		right 0
		left 0
		bottom 12px
		text-align center
		font-size 0
		.dot
			display inline-block
			margin 0 4px
			width 8px
			height 8px
			border-radius 50%
			background $color-text-l
			&.active
				width 20px
				border-radius 5px
				background $color-text-ll
</style>
